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Possible Discovery of X-ray Emission from Supernova 2017egm with Swift

ATel #10499; Dirk Grupe (Morehead State University), Subo Dong (KIAA-PKU), Jose L. Prieto (Universidad Diego Portales), & David Pooley (Trinity University)
on 16 Jun 2017; 17:24 UT
Credential Certification: Dirk Grupe (dgrupe007@gmail.com)

Subjects: X-ray, Supernovae

Referred to by ATel #: 10531, 10538, 10546

We report of the discovery of X-ray emission possibly associated with the GAIA-discovered supernova 2017egm (Delgado et al, TNS Astronomical Transient Report No 11679), which has been recently been identified as a hydrogen-poor super-luminous supernova (SLSN-I, Dong et al., ATEL #10498). Swift observed the field of SN 2017egm between 2017-June-02 06:54 and 2017-June-15 09:09 11 times for a total of 12988s. There is clearly an enhanced X-ray emission within the source extraction region centered on the optical position of SN 2017egm (10 19 05.62, +46 27 14.1). The position of this X-ray source is RA-2000: 10 19 05.77, Dec-2000=+46 27 18.6 with an uncertainty of 5.1". This position is 4.6" away for the optical position of SN 2017egm. However, the host galaxy of SN 2017egm, NGC 3191, is a star forming galaxy. The central position of NGC 3191 is 7.3" from the position of the X-ray source. Although the optical position of SN 2017egm is closer to the position of the X-ray source, we can not entirely exclude the possibility of the star forming region in NGC 3191 being the cause for the X-ray emission. Applying the Bayesian method described in Kraft et al (1991), we obtained a count rate of the X-ray source in the 0.3 - 10 keV band in the Swift XRT of (9.5+3.2-2.70)e-4 counts/s which corresponds to a 0.3-10 keV flux of about (4.7+1.6-1.4)e-17 W m^-2 (e-14 ergs/s/cm2). Assuming that the X-ray source is associated with NGC 3191 (z=0.0307, D=135 Mpc) the luminosity of the X-ray source is 1e34 W (1e41 ergs/s). Due to the ambiguity of associating the X-ray source clearly with either supernova 2017egm or the star forming region in NGC 3191, Chandra has been triggered for a deeper observation (PI Pooley). Note, that NGC 3191 has never been observed by Chandra or XMM, nor has it been detected by ROSAT.